This set of Object Oriented Programming (OOPs) using C++ Multiple Choice Questions & Answers (MCQs) focuses on “Upcasting”.
1. What is upcasting?
a) Casting subtype to supertype
b) Casting super type to subtype
c) Casting subtype to super type and vice versa
d) Casting anytype to any other type
View Answer
Explanation: The upcasting concept includes only the casting of subtypes to the super types. This casting is generally done implicitly. Smaller size types can fit into larger size types implicitly.
2. Which among the following is true for upcasting in inheritance?
a) Downward to the inheritance tree
b) Upward to the inheritance tree
c) Either upward or downward
d) Doesn’t apply on inheritance
View Answer
Explanation: The upcasting concept in inheritance is always applied upward the inheritance tree. The derived class objects can be type casted to any of its parent class type. Since is a relationship applies in general inheritance.
3. Which among the following is safe?
a) Upcasting
b) Downcasting
c) Both upcasting and downcasting
d) If upcasting is safe then downcasting is not, and vice versa
View Answer
Explanation: The upcasting is always safe since the derived type or the smaller type is converted into the base type or the larger size. This results in allocating a smaller size data into bigger type data. No data is lost in casting, hence safe.
4. Which among the following is the best situation to use upcasting?
a) For general code dealing with only subtype
b) For general code dealing with only supertype
c) For general code dealing with both the supertype and subtype
d) For writing a rigid code with respect to subtype
View Answer
Explanation: When a general code has to be written where we use only the supertype object or the data of bigger size, then upcasting would be the best option. Since the whole code will require only the supertype name references.
5. Which property is shown most when upcasting is used?
a) Code reusability
b) Code efficiency
c) Complex code simple syntax
d) Encapsulation
View Answer
Explanation: The code written using upcasting mostly shows complex code in simpler syntax features. This is because the upcasting concept can be applied as polymorphism and to group the similar type of objects.
6. Upcasting and downcasting objects are the same as casting primitive types.
a) True
b) False
View Answer
Explanation: It is a bit confusing concept since both casting concepts are different. Primitive casting depends on the type and size of data being typecast. Whereas in objects casting, the classes and inheritance order plays a big role.
7. Which casting among the following is allowed for the code given below?
class A { public :int a; } class B:public A { int b; } main() { B b=new A(); //casting 1 A a=new B(); //casting 2 }
a) Casting 1
b) Casting 2
c) casting 1 and casting 2
d) casting 1 nor casting 2
View Answer
Explanation: The casting 2 is correct. The objects casting must be done from derived class object to a parent class object. That is, the object of the superclass can be made an object of subclass only. Vice versa is not possible.
8. If multiple inheritance is implemented, which upcasting will be correct?
a) Upcast to first base class listed in inheritance
b) Upcast to send base class listed in inheritance
c) Upcast to any base class
d) Upcast is not possible
View Answer
Explanation: The upcasting of derived class object is possible to any base class. This is because the base class object can represent any of its derived classes using upcasting.
9. If class C inherits class B and class B inherits class A ________________
a) Class C object can be upcasted to object of class B only
b) Class C object can be upcasted to object of class A only
c) Class C object can be upcasted to object of either class A or B
d) Class C object can’t be upcasted
View Answer
Explanation: Both class A and B are parent classes of class C. Class C object hence can be upcasted to any of those class objects. It is not compulsory to upcast to nearest parent.
10. Upcasting is _____________________ without an explicit type cast.
a) Always allowed for public inheritance
b) Always allowed for protected inheritance
c) Always allowed for private inheritance
d) Not allowed
View Answer
Explanation: The public inheritance shows the most flexible is-a relationship. Hence explicit type casting is not required. Implicit type casting is done by the compiler.
11. Which concept is needed because of implicit type casting use?
a) Static binding
b) Dynamic binding
c) Compile time binding
d) Source code binding
View Answer
Explanation: Since the implicit type casting allows casting of a base class pointer to refer to its derived class object or even base class object. We need dynamic type casting so that the references can be resolved during execution of program.
12. When are the pointer types known for upcasting the objects?
a) Compile time
b) Runtime
c) Source code build time
d) Doesn’t apply to pointer types
View Answer
Explanation: The pointer or reference types are known at compile time for the upcasting of an object. This is because the addresses must be known for casting the derived class to base class object.
13. When are the object type known for upcasting the objects?
a) Compile time
b) Runtime
c) Source code build time
d) Doesn’t apply to objects directly
View Answer
Explanation: The upcasting with objects directly requires runtime resolving. The objects are fixed and address are allocated at compile time. But the execution of a program requires runtime knowledge of object types, for implicit type cast.
14. If two classes are defined “Parent” and “Child” then which is the correct type upcast syntax in C++?
a) Parent *p=child;
b) Parent *p=*child;
c) Parent *p=&child;
d) Parent *p=Child();
View Answer
Explanation: The syntax must contain the base class name first. So that the parent class object pointer can be declared. Then the object is assigned with the derived class object with & symbol. & symbol is added to get the address of the derived class object.
15. Which among the following is true?
a) Upcasting is possible only for single level inheritance
b) Upcasting is possible only for multilevel inheritance
c) Upcasting is possible only for multiple inheritance
d) Upcasting is possible for any type of inheritance
View Answer
Explanation: The type of inheritance doesn’t matter with the upcasting concept. Upcasting applies to all types of inheritance. Any derived class object can be upcasted to any of its base class object.
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